The present invention relates to the carrying of data frame traffic over a synchronous digital network.
Historically, the telecommunications industry has developed separately and largely independently from the computing industry. Conventional telecommunications systems are characterized by having high reliability circuit switched networks for communicating over long distances, whereas data communications between communicating computers is largely based upon shared access packet communications.
Datacoms may operate over a local area, to form a local area network (LAN) or over a wide area to form a wide area network (WAN). Historically the difference between a LAN and a WAN is one of geographical coverage. A LAN may cover communicating computing devices distributed over an area of kilometers or tens of kilometers, whereas a WAN may encompass communicating computing devices distributed over a wider geographical area, of the order of hundreds of kilometers or greater.
Conventional local area networks are generally taken to be digital data networks operating at rates in excess of 1 MBits/s over distances of from a few meters up to several kilometers. Conventional local area networks are almost universally serial systems, in which both data and control functions are carried through the same channel or medium. Local area networks are primarily data transmission systems intended to link computer devices and associated devices within a restricted geographical area. However, many local area networks include speech transmission as a service. A plurality of computer and associated devices linked together in a LAN may range from anything from a full-scale mainframe computing system to small personal computers. Since a local area network is confined to a restricted geographical area, it is possible to employ vastly different transmission methods from those commonly used in telecommunications systems. Local area networks are usually specific to a particular organization which owns them and can be completely independent of the constraints imposed by public telephone authorities, the ITU, and other public services. Local area networks are characterized by comprising inexpensive line driving equipment rather than the relatively complex modems needed for public analogue networks. High data transmission rates are achieved by utilizing the advantages of short distance.
Conventional wide area networks operate in general on a greater scale than local area networks. A wide area network is generally employed whenever information in electronic form on cables leaves a site, even for short distances. Data transmission rates involved are generally between a few hundred and a few thousand bits per second, typically up to 50 kilobits per second. The distances involved in a wide area network are from around 1 kilometer to possible thousands of kilometers, and error rates are greater than with local area networks. Wide area networks are generally carried over public telecommunications networks.
The distinction between networks which have historically been considered to be local area networks and those which have been considered to be wide area networks is becoming increasingly blurred.
Because conventional telecoms systems have developed in parallel with conventional datacoms systems, there is a significant mis-match in data rates between conventional datacoms protocols as used in LANs and WANs, and conventional telecoms protocols. In general, telecoms operators provide equipment having standard telecoms interfaces, for example E1, T1, E3, T3, STM-1, which are used by the datacoms industry to provide wide area network point to point links. However, this is inconvenient for datacoms providers since datacoms protocols have developed using a completely different set of interfaces and protocols, for example carrier sense multiple access collision detection CSMA/CD systems, subject of IEEE standard 802.3, and Ethernet which is available in 10 MBits/s, 100 MBits/s and 1 GigaBits/s versions. Conventional datacoms protocols do not match up very well to conventional telecoms interfaces because of a mis-match in data rates and technologies between conventional datacoms and conventional telecoms.
Several prior art attempts have been made to carry frame based data over telecoms networks. Prior art systems for incorporating frame based data over synchronous networks include schemes which contain Ethernet data frames in asynchronous transfer mode (ATM) cells which are then transported in a plesioscynchronous mode and which may then be transported according to ITU-T recommendation G.708 in a synchronous digital hierarchy (SDH) network. In this scheme, known as IMA (Inverse multiplexing of ATM), conceived by the ATM Forum, an ATM circuit is divided and input into a plurality of E1 circuits. This enables an ATM signal to be carried across a legacy network, for example a plesiosynchronous digital hierarchy (PDH) network. Ethernet frames are included as the payload of the ATM cells, which are then carried via the E1 circuits over a conventional PDH network. However, this prior art scheme has a disadvantage of a high packetization header overhead, which can comprise up to 20% of the SDH payload.
Another prior art system aimed at carrying frame based data over synchronous digital networks is the conventional Ethernet remote bridge. This system is based on the known PPP protocol, for example, as implemented by the packet on Sonet (POS phy) system of PMC Sierra. However, in this scheme, a high packetization overhead is present and packaging delays are relatively high.
Manufacturers such as CISCO, and Bay Networks produce equipment for both of the above mentioned inverse multiplexing of ATM, and Ethernet bridge systems.
A further prior art scheme uses a plurality of fiber optic repeaters to provide native Ethernet rate connections between a customer premises and a LAN switch. However, this solution dedicates a whole fiber to Ethernet rate, which is an inefficient use of the fiber optic cable resources.
One object of the present invention is to provide high data rate, high reliability functionality available with conventional local area networks, but over a wide area network transported on a long distance high capacity synchronous digital network.
Another object of the present invention is to overcome data rate mis-matched between conventional datacoms systems and conventional telecommunications systems in an efficient manner.
Another object of the present invention is to incorporate frame based data directly into a synchronous digital hierarchy payload, without encapsulation in an ATM cell or other intermediate carrier.
Another object of the present invention is to incorporate frame based data into a synchronous network without incurring high processing delays, and without incurring a high packetization header overhead.
According to one aspect of the present invention, there is provided a frame based data communications network comprising:
a plurality of computer devices each having a frame based data channel interface;
a plurality of synchronous multiplexers, each having a frame based data channel interface and a synchronous digital communications port, and capable of interfacing between a frame based data protocol and a synchronous digital network protocol;
wherein said plurality of computing devices communicate with each other over a plurality of frame based data channels, said frame based data channels carried over a synchronous digital transport network connecting said plurality of synchronous multiplexers.
Preferably, said frame based channel interface interfaces directly between said frame based data protocol and said synchronous digital network protocol without traversing any intermediate protocols.
Preferably, said frame based data channel interface comprises: means for mapping a data frame of said frame based data channel to at least one payload of said synchronous network protocol.
The synchronous digital transport network may comprise a synchronous digital hierarchy (SDH) network in accordance with ITU-T G70.X, an example of which is the synchronous optical network (SONET) in accordance with ITU-T recommendation G.708 and related recommendations.
Synchronous multiplexers may comprise add-drop multiplexers, or terminal multiplexers.
According to a second aspect of the present invention, there is provided a synchronous digital multiplexer comprising:
a plurality of telecoms tributary interfaces;
a frame based data channel interface; and
a synchronous digital channel port.
By providing a plurality of telecoms tributaries in addition to a frame based data access port in a synchronous multiplexer, frame based data channels may be entered directly into synchronous digital hierarchy virtual container payloads in an efficient manner.
Preferably said frame based channel interface comprises:
a frame based data channel physical port;
a frame based data channel switch communicating with said frame based data channel physical port;
a rate adaption means for converting data at a frame based data channel rate into a bitstream of a data rate capable of being carried in at least one virtual container; and
a synchronous digital network payload mapper for mapping said bitstream into said at least one virtual container.
According to a third aspect of the present invention there is provided a method of communicating frame based data over a synchronous digital network comprising the steps of:
modifying a data rate of said frame based data to a rate compatible with a synchronous digital network virtual container; and
inputting said rate adapted frame based data directly into at least one said synchronous digital network virtual container.
Preferably said method comprises the steps of:
concatenating a plurality of said virtual containers together; and
containing a said data frame into said plurality of concatenated virtual containers.
The invention includes a method of creating a frame based data channel within a synchronous digital channel comprising the steps of:
modifying a data rate of said frame based data outside said synchronous digital channel to a rate compatible with said synchronous digital channel; and
mapping said rate adapted frame based data directly to said synchronous digital channel.
Said step of mapping preferably comprises containing said modified data frame based data into at least one virtual container.
The invention includes a communications network comprising:
a plurality of network components supporting an OSI layer 2 frame based data channel;
a plurality of network components supporting at least one synchronous digital channel; and
a plurality of network components capable of transferring data frames of said OSI layer 2 data channel directly into and out of a plurality of payloads of said at least one synchronous digital channel.
The invention includes a data communications network comprising:
a plurality of network devices each comprising: an OSI layer 2 frame switching device; a rate adaption device for adapting a data rate between an OSI layer 2 data rate and a synchronous transmission data rate; and a mapping device for mapping data between said OSI layer 2 frame switch and a synchronous digital channel;
wherein said plurality of mapping devices communicate over said synchronous digital channel; and
said plurality of OSI layer 2 frame switching devices communicate over an layer 2 channel carried on said synchronous digital network.
Said OSI layer 2 channel may comprise a ring channel linking said plurality of network devices.
Said OSI layer 2 channel may comprise a plurality of point to point channels linking pairs of individual said OSI layer 2 frame switches.
The invention includes a communications network comprising:
a plurality of network devices each comprising: a rate adaption device for adapting a data rate between an OSI layer 2 data rate and a synchronous transmission data rate; and a mapping device for mapping data between an OSI layer 2 channel and a synchronous digital channel;
wherein said plurality of mapping means communicate over said synchronous digital channel; and
said plurality of rate adaption means communicate over said OSI layer 2 channel carried on said synchronous digital channel.
Said OSI layer 2 channel may comprise a ring channel.